This invention relates generally to the generation and the provision of refrigeration and is particularly advantageous for use with a multicomponent refrigerant fluid.
Refrigeration is used extensively in the freezing of foods, cryogenic rectification of air, production of pharmaceuticals, liquefaction of natural gas, and in many other applications wherein refrigeration is required to provide cooling duty to a refrigeration load.
A recent significant advancement in the field of refrigeration is the development of refrigeration systems using multicomponent refrigerants which are able to generate refrigeration much more efficiently than conventional systems. These refrigeration systems, also known as mixed gas refrigerant systems or MGR systems, are particularly attractive for providing refrigeration at very low or cryogenic temperatures such as below xe2x88x9280xc2x0 F.
A number of problems arise when small scale MGR systems are increased to industrial scale. An advantage inherent in a mixed refrigerant cycle is that the saturation temperature increases as more of the liquid phase is vaporized, producing a temperature glide. This allows refrigeration over a wide temperature range. If the cross sectional area provided for flow is too high the difference between the vapor and liquid velocity will be great. If liquid velocity is very low, or liquid ceases to flow, then the local equilibrium between vapor and liquid will be lost in favor of equilibrium between a large region of liquid and the vapor generated from its surface. This is termed xe2x80x9cpool boilingxe2x80x9d or xe2x80x9cpot boilingxe2x80x9d, and is the cause of a degradation in performance.
To avoid pool boiling the vapor velocity must be high, so the optimum design of the heat exchanger is such that its height greatly exceeds its width. The problem with a long thin heat exchanger is that the cold box package containing the system must be very tall. Tall heat exchangers are a particular problem when the system must be installed indoors. A good example of an indoor system is a mixed gas refrigerant system used for food freezing.
Another problem occurs in positioning the aftercooler relative to a tall main heat exchanger. If the aftercooler is situated on top of the main heat exchanger then the overall system height is increased, and expensive mechanical support is required. If the aftercooler is located on the ground it is necessary to transfer a two-phase liquid and vapor mixture to the top of the main heat exchanger. This second option greatly increases the system pressure loss, and in turn the electrical power consumption of the compressor required to drive the refrigerant flow. A third option is to separate the liquid and vapor phases at ground level, with the liquid being separately pumped to the top of the main heat exchanger. However, this introduces equipment with moving parts and is generally undesirable.
Yet another problem concerns drainage of refrigerant when a refrigeration system involving internal recycle of liquid is shut down. Such cycles typically are used to provide refrigeration below 120K. It is critical that heavier components of the mixture (i.e. those with low volatility) have a low concentration in the coldest region of the heat exchanger. This is because they can freeze and block the passages of the heat exchanger. In a conventional system the warm end of the process is at the top of the heat exchanger so the heavy components, in liquid form, drain naturally towards the lowest (coldest) point. To prevent this check valves are sometimes used, but check valves are problematic due to leakage and other difficulties.
Accordingly, it is an object of this invention to provide an improved refrigeration system which may be effectively employed with a multicomponent refrigerant fluid.
It is another object of this invention to provide an improved refrigeration system which can be effectively operated on an industrial scale while overcoming problems experienced with conventional systems especially when a multicomponent refrigerant fluid is employed.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for providing refrigeration to a refrigeration load comprising:
(A) compressing a warm refrigerant fluid, and cooling the compressed refrigerant fluid by upward flow through a first heat exchanger section;
(B) further cooling the cooled refrigerant fluid by downward flow through a second heat exchanger section, expanding the further cooled refrigerant fluid to generate refrigeration, and providing refrigeration from the refrigeration bearing refrigerant fluid to a refrigeration load;
(C) warming the resulting refrigerant fluid by indirect heat exchange with the further cooling refrigerant fluid; and
(D) further warming the resulting refrigerant fluid by indirect heat exchange with the cooling compressed refrigerant fluid to produce said warm refrigerant fluid.
Another aspect of the invention is:
A dual section refrigeration system comprising:
(A) a first vertically oriented heat exchanger section, a compressor, and means for passing refrigerant fluid from the compressor to the bottom of the first vertically oriented heat exchanger section;
(B) a second vertically oriented heat exchanger section, and means for passing refrigerant fluid from the top of the first vertically oriented heat exchanger section to the top of the second vertically oriented heat exchanger section;
(C) an expansion device, means for passing refrigerant fluid from the bottom of the second vertically oriented heat exchanger section to the expansion device, and means for passing refrigerant fluid from the expansion device to the bottom of the second vertically oriented heat exchanger section; and
(D) means for passing refrigerant fluid from the top of the second vertically oriented heat exchanger section to the top of the first vertically oriented heat exchanger section, and means for passing refrigerant fluid from the bottom of the first vertically oriented heat exchanger section to the compressor.
As used herein the term xe2x80x9crefrigeration loadxe2x80x9d means a fluid or object that requires a reduction in energy, or removal of heat, to lower its temperature or to keep its temperature from rising.
used herein the term xe2x80x9cexpansionxe2x80x9d means to effect a reduction in pressure.
As used herein the term xe2x80x9cexpansion devicexe2x80x9d means apparatus for effecting expansion of a fluid while work expanding the fluid to generate refrigeration.
As used herein the term xe2x80x9ccompressorxe2x80x9d means apparatus for effecting compression of a fluid.
As used herein the term xe2x80x9cmulticomponent refrigerantxe2x80x9d means a fluid comprising two or more species and capable of generating refrigeration.
As used herein the term xe2x80x9crefrigerationxe2x80x9d means the capability to absorb heat from a subambient temperature system and to reject it at a superambient temperature.
As used herein the term xe2x80x9crefrigerantxe2x80x9d means fluid in a refrigeration process which undergoes changes in temperature, pressure and possibly phase to absorb heat at a lower temperature and reject it at a higher temperature.
As used herein the term xe2x80x9csubcoolingxe2x80x9d means cooling a liquid to be at a temperature lower than the saturation temperature of that liquid for the existing pressure.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cphase separatorxe2x80x9d means a vessel wherein incoming fluid is separated into individual vapor and liquid fractions. Typically the vessel has sufficient cross sectional area so that the vapor and liquid are separated by gravity.
As used herein the terms xe2x80x9cupward flowxe2x80x9d and xe2x80x9cdownward flowxe2x80x9d encompass substantially upward flow and downward flow as would occur in a crossflow arrangement.